Generally, a combustor for generating combustion gas includes a combustion burner for supplying a combustion space with fuel and an oxidant such as air to form flames. For instance, some combustors for a gas turbine are equipped with a premix combustion burner. A premix combustion burner includes an axial flow path formed radially outside a nozzle. Premix gas containing compressed air and fuel flows through the axial flow path. In a combustion burner of this type, a swirler is usually provided in the axial flow path to promote premix in many cases.
Meanwhile, it is known that the position of flames formed by a combustion burner is determined by a balance between the combustion velocity, which is a propagating velocity of the flames, and the axial-flow velocity of the gas flowing through the axial flow path. During normal combustion, flames are maintained at a position offset toward the downstream side from the combustion burner by a predetermined distance. However, in a case where the combustion burner includes a swirler, flashback (backfire) may occur, in which flames run backward toward the combustion burner. The flashback occurs due to the axial-flow velocity being lower in a region formed at the center of the swirl of the swirl flow formed by the swirler than in the surrounding region, and the combustion velocity exceeding the axial-flow velocity in this region with the lower axial-flow velocity to cause the flames to propagate excessively to the combustion burner. Frequent occurrence of flashback may bring about troubles such as damage due to burn of the combustion burner.
In view of this, to prevent flashback, the premix combustion burner described in Patent Document 1, for instance, includes a cutout on a rear edge at the radially inner side of a swirl vane. With such a premix combustion burner, a swirl air flow is formed along a curved surface at the radially outer side of the swirl vane. On the other hand, at the radially inner side of the swirl vane, compressed air flows downstream in the axial direction of the combustion burner through the cutout, and thus the axial-flow velocity increases at the radially inner side of the swirl vane (at the center of the swirl of the swirl flow). Further, as a technique related to the above, described in Patent Document 2 is a burner including a partition wall partitioning an air channel region at the radially inner side from an air channel region at the radially outer side, and swirl vanes disposed in the air channel region at the radially outer side. With this burner, air is not swirled in the air channel region at the radially inner side, so as to increase the axial-flow velocity at the inner side.